2026-06-18 コロンビア大学
＜関連情報＞
- https://news.climate.columbia.edu/2026/06/18/carbon-dioxide-and-water-played-key-roles-in-historic-mount-etna-eruptions/
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2026GC012924
紀元前122年のエトナ山の苦鉄質プリニー式噴火は、深部起源で浅部噴火だった Deep Origin and Shallow Launch for the Etna 122 B.C. Mafic Plinian Eruption
M. Gavrilenko, E. Gazel, K. Dayton, A. Barth, T. Plank, E. G. Huggins, B. Houghton
Geochemistry, Geophysics, Geosystems Published: 02 June 2026
DOI:https://doi.org/10.1029/2026GC012924
Abstract
Basaltic Plinian eruptions challenge our understanding of explosive volcanism. The 122 B.C. Plinian eruption of Etna ranks among the most powerful mafic explosive events known. Here, we combine volatile barometry of 122 B.C. from olivine-hosted melt and fluid inclusions with comparative data from the sub-Plinian Fall Stratified eruption at Etna (3930 BP) to assess the storage depths and degassing paths that govern explosive eruptive styles. Our results indicate that the 122 B.C. magma storage started deep (∼22 km) within Etna’s plumbing system, had a complex ascent history, and was finally stored pre-eruptively at shallow levels (∼2–5 km) for a minimum of ∼3 weeks, resulting in low equilibrated H2O (∼2 wt%) and CO2 (≤500 ppm in bubble-free melt inclusions) contents. The Fall Stratified event, in contrast, records deeper storage (∼24–30 km), high magmatic volatile contents (CO2 concentrations up to 9600 ppm, H2O concentrations up to 6.3 wt%), and exceptionally rapid magma ascent rates (17.5 m/s). We propose that the 122 B.C. eruption likely resulted from multiple episodes of replenishment by basaltic magma with a much lower CO2 concentration (<4,500 ppm) than that of the Fall Stratified event. The eruption was probably triggered by an increase in magma effective viscosity due to extensive microlite crystallization at shallow levels, which caused a secondary vesiculation event. This mechanism contrasts with mantle-derived eruptions such as the Fall Stratified event, where deep volatile-exsolution, controlled by CO2, is thought to drive the eruption.
Plain Language Summary
Highly explosive volcanic eruptions are typically associated with high-silica magmas, but on rare occasions, lower-silica basaltic magmas can also supply violent eruptions. One of the strongest known examples in record is the 122 B.C. eruption of Mount Etna in Italy. Here, we analyze tiny pockets of trapped melt and fluid preserved inside crystals to constrain where magma was stored before eruption and elucidate how it traveled toward the surface. We found that the 122 B.C. magma rose from deep within the Earth but then paused and slowly released gas at shallow depths for at least several weeks before erupting. During this time, small crystals formed, increasing magma viscosity and allowing gases to accumulate, which ultimately led to an explosive eruption. This behavior contrasts strongly with another explosive eruption at Etna, the Fall Stratified event, in which magma rose extremely quickly from deeper levels because it contained unusually large amounts of gas. Our results show that violent basaltic eruptions can occur through different processes. Recognizing these differences is important for understanding volcanic behavior and for the improvement of risk assessment at active volcanoes.
